A verification code, CAPTCHA (“Completely Automated Public Turing test to tell Computers and Humans Apart”) is a public fully automatic program for distinguishing a user is a computer or a human being. The verification code may effectively prevent a client from cracking user's password with malicious attack using a machine, so as to effectively reduce system security risk. FIG. 1A is a schematic diagram illustrating a typical verification method using character verification. FIG. 1B is a schematic diagram illustrating a typical verification method using image verification. The principle of the verification methods shown in FIG. 1A and 1B is that the server has recorded the metadata of the shown image, and with the shown image, the client machine can hardly retrace the meaning of the image, but human eyes and human brain can easily recognize the meaning of the image, therefore the client is a human being or a machine may be effectively distinguished, so as to prevent a client machine from cracking passwords with malicious attack.
With the development of flexible material, the flexible display screens start to emerge in the market. FIG. 2A and FIG. 2B are schematic diagrams illustrating a handheld device with a flexible display screen. With the gradual improvement of the flexibility of the flexible display screen, the shape of the flexible screen is more and more flexible, as shown in FIG. 2B, the flexible display screen may be fully folded.
Typically , the verification method based on a flexible display screen is the same with the verification method based on a non-flexible display screen, which doesn't make full use of the deformable and bendable property of the flexible display screen to achieve the verification.